Encoded content requires a “decoding” process in order to use the content. Some examples of encoded content include MPEG-1 MPEG-2 H.264/AVC, WMA, MPEG4, JPEG2000, MP3, PDF, Windows Word, Postscript, etc., and their encrypted versions.
The prior art methods for watermarking encoded content comply with the media transform with many restrictions such as no watermarking in some I-frames or no watermark in the first ten seconds of the digital media. The prior art methods also do not apply media transforms and watermarking to every I-frame in order to support “trick play” such as fast forwarding. Media transform is a process to replace sets of bits in the encoded content with other sets of bits. In some cases, the second set of bits represents a better quality of the content than the first set of bits. As a result, the media transform process improves the quality of the content. Furthermore, in some cases the second set of bits may contain additional digital watermark signals and, thus, such process may introduce digital watermarks.
If no media transform occurs in some part of an encoded content, for example, in one out of every four frames of video I-frame data, it unduly restricts the space for watermarking resulting in embedding less watermark payload and increasing synchronization costs during watermark detection. Furthermore, such restriction may cause significant portions of the content to be unwatermarked/unprotected. It is clear that there needs to be a method for protecting digital content while preserving specialty playback device operations, such as “trick play”.